PHOENIX — J. D. Hayworth is a large man, and to compensate for his indulgences, he hits the elliptical trainer every morning at 4, zipping along to an incongruous soundtrack of Elvis Costello, Frank Sinatra and old advertising jingles.

Until recently, he would then repair to a local radio station, where he would spend the better part of the day denouncing, in no particular order, illegal immigrants, all things Barack Obama, those who are insufficiently patriotic and, his favorite mark, one John McCain, the senior senator from Arizona.

Now, Mr. Hayworth, a former Republican congressman, is preparing to expand his political appetite for Mr. McCain by formally announcing next week what everyone in this state has known for months: his challenge to the senator in the Republican primary in August.

Mr. Hayworth hopes that by standing at the intersection of opportunity and timing, he can lure enough Tea Party sympathizers fresh off their convention in Nashville, seducible independent voters (Arizona has an open primary) and conservative Republican grass-roots activists, who have long been disenchanted with Mr. McCain.

“The political winds of change are here,” Mr. Hayworth, 51, said over lunch. “The conservatives are highly motivated, and there is an intensity level among conservatives to take part in this primary. The atmospherics will help us.”